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Schweitzer Engineering Laboratories SEL-787 - Figure 2.21 SEL-787 Provides Two-Winding Transformer Differential Protection with REF and Voltage-Based Protection

Schweitzer Engineering Laboratories SEL-787
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2.23
Date Code 20081022 Instruction Manual SEL-787 Relay
Installation
AC/DC Control Connection Diagrams
Installing the optional 1 ACI/3 AVI voltage/current card in Slot E of the SEL-787 provides neutral current and REF
protection, as well as three-phase voltage inputs. These voltage inputs provide the relay with 20.0 to 70.0 Hz frequency
tracking, over-/undervoltage elements, frequency elements, power elements, and volts-per-hertz protection of the
transformer.
Refer to Figure 2.23, which illustrates tripping control of the two-power circuit breakers.
Figure 2.21 SEL-787 Provides Two-Winding Transformer Differential Protection With REF and Voltage-Based
Protection
VA VB VC VN
IAW1
IBW1
ICW1
IAW2
IBW2
ICW2
SEL-787 Relay
52-1
52-2
A B C
a b c
IN
A
B
C
a
b
c
200/5 A
138 kV
30 MVA
13.8 kV
2000/5 A
Note: The CT secondary circuit must be grounded in the relay

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